I have a 505 "refurb" G4 (3rd one!). Recently it had been lagging terribly. It had become painfully to use because of all the freezing. I should add that I do have a lot of apps on this phone. I didn't want to go through another factory reset, so I cleared the app cache. Amazingly I haven't seen one stutter since. Everything works perfectly again. Just thought I would share this.